linux-kernel - [PATCH v2] kvm: x86: Limit the number of "kvm: disabled by bios" messages

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Message-Id: <20200227180047.53888-1-e.velu@criteo.com>
Date:   Thu, 27 Feb 2020 19:00:46 +0100
From:   Erwan Velu <erwanaliasr1@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Erwan Velu <e.velu@...teo.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        kvm@...r.kernel.org (open list:KERNEL VIRTUAL MACHINE FOR X86 (KVM/x86)),
        linux-kernel@...r.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND
        64-BIT))
Subject: [PATCH v2] kvm: x86: Limit the number of "kvm: disabled by bios" messages

In older version of systemd(219), at boot time, udevadm is called with :
	/usr/bin/udevadm trigger --type=devices --action=add"

This program generates an echo "add" in /sys/devices/system/cpu/cpu<x>/uevent,
leading to the "kvm: disabled by bios" message in case of your Bios disabled
the virtualization extensions.

On a modern system running up to 256 CPU threads, this pollutes the Kernel logs.

This patch offers to ratelimit this message to avoid any userspace program triggering
this uevent printing this message too often.

This patch is only a workaround but greatly reduce the pollution without
breaking the current behavior of printing a message if some try to instantiate
KVM on a system that doesn't support it.

Note that recent versions of systemd (>239) do not have trigger this behavior.

This patch will be useful at least for some using older systemd with recent Kernels.

Signed-off-by: Erwan Velu <e.velu@...teo.com>
---
 arch/x86/kvm/x86.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 359fcd395132..c8a90231befe 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7308,12 +7308,12 @@ int kvm_arch_init(void *opaque)
 	}
 
 	if (!ops->cpu_has_kvm_support()) {
-		printk(KERN_ERR "kvm: no hardware support\n");
+		pr_err_ratelimited("kvm: no hardware support\n");
 		r = -EOPNOTSUPP;
 		goto out;
 	}
 	if (ops->disabled_by_bios()) {
-		printk(KERN_ERR "kvm: disabled by bios\n");
+		pr_err_ratelimited("kvm: disabled by bios\n");
 		r = -EOPNOTSUPP;
 		goto out;
 	}
-- 
2.24.1